Simple library for using the system's monotonic clock. This library is
geared toward programs that need to run for long periods of time. It does
not (necessarily) provide high-resolution timing.

On Windows, this uses GetTickCount64, but falls back to
GetTickCount if it is not available. GetTickCount64 was
introduced in Windows Vista and Windows Server 2008.
Support for QueryPerformanceCounter is also available, but is not
used by default, as it is less accurate in the long run than
GetTickCount.